Heretofore, a seal ring of this type has been employed in hydraulic devices, for example, the automatic transmission of an automobile.
Now, a seal ring according to a prior-art technique will be explained with reference to FIGS. 34 and 35.
FIG. 34 is a planar model view of the seal ring according to the prior-art technique, while FIG. 35 is a model-like sectional view showing the mounted state of the seal ring according to the prior-art technique.
The illustrated seal ring 100 serves to seal the annular interspace between a housing 200 provided with a shaft hole and a shaft 300 inserted in the shaft hole, and it is used in a state where it is mounted within an annular groove 301 provided in the shaft 300.
The seal ring 100 is formed of a resin material, and it includes a first seal portion 101 for sealing the sidewall surface of the annular groove 301 provided in the shaft 300, and a second seal portion 102 for sealing the inner peripheral surface of the shaft hole provided in the housing 200.
Herein, when a pressure acts in the direction of an arrow P in FIG. 35, from the sealed fluid side O toward the unsealed fluid side A, the seal ring 100 is urged onto the unsealed fluid side A, and hence, the first seal portion 101 urges the sidewall surface of the annular groove 301, while the second seal portion 102 urges the inner peripheral surface of the shaft hole provided in the housing 200 and opposing to the annular groove 301, so as to seal the surfaces at the positions of the respective seal portions.
In this way, the sealed fluid has been prevented from leaking onto the unsealed fluid side A.
Here, the sealed fluid is, for example, lubricating oil, and it signifies ATF especially in a case where the seal ring is utilized for the automatic transmission of an automobile.
Besides, as shown in FIG. 34, the ring body of the seal ring 100 is provided with a separation portion So at one part in the circumferential direction thereof for the purposes of enhancing an assemblability, etc.
Various aspects have been known as such a separation portion So, and a special step cut in the shape of two steps has been known as an aspect capable of suitably coping even with the change of an ambient temperature.
According to the special step cut, the wall surfaces of the ring body in the circumferential direction thereof come into close contact with each other, so that the sealed fluid can be prevented from leaking. Moreover, owing to a construction wherein the seal ring cuts off the sealed fluid side and the unsealed fluid side while the surfaces of the ring body perpendicular to the circumferential direction define gaps in the circumferential direction therebetween, even when the seal ring has relatively moved in the circumferential direction on account of the discrepancy of the coefficients of linear expansion attributed to the different materials of the seal ring and the housing, the variations of dimensions can be absorbed in correspondence with the gaps while a tightly enclosing state is kept, so that the seal ring can suitably maintain a tightly enclosing performance even against the ambient temperature change.
In such a seal ring 100, especially in a case where the shaft 300 is of an aluminum alloy or the like soft material, especially the sidewall surface of the annular groove 301 has worn away on account of the slide between the first seal portion 101 and the sidewall surface of the annular groove 301, which is ascribable to the relative rotation between the seal ring 100 and the shaft 300.
This is because a lubricating film based on the lubricating oil is difficult to be formed between the first seal portion 101 and the sidewall surface of the annular groove 301. Especially in a case where any foreign matter existent in the lubricating oil has been bitten between the first seal portion and the sidewall surface, or where the accumulation of wear powder, or the like has occurred, the wear becomes intense. Also, in a case where the seal ring 100 has been used under a high pressure and at a high rotational speed, the first seal portion 101 and the sidewall surface of the annular groove 301 become a high temperature on account of the relative rotation between the seal ring 100 and the shaft 300, and the seal ring 100 is sometimes molten.
As a technique for reducing such wear, there has been known one wherein a slot which serves to feed the lubricating oil being the sealed fluid between the first seal portion 101 and the sidewall surface of the annular groove 301 is provided, thereby to form a lubricating film and to enhance a wear-proofness (for example, JP-A-9-96363).
FIG. 36 shows model diagrams of a seal ring according to a prior-art technique, wherein FIG. 36A is a model-like partial plan view, FIG. 36B is a sectional view taken along b-b in FIG. 36A, and FIG. 36C is a side view seen in an I-direction in FIG. 36A.
As shown in FIG. 36, the first seal portion 101 is provided with the communicating slot 101a for communicating the sealed fluid side O with the unsealed fluid side A, whereby the lubricating oil on the sealed fluid side O is caused to leak into the communicating slot 101a. Thus, when the first seal portion 101 has come into sliding contact with the sidewall surface of the annular groove 301, the lubricating film is formed between them, to improve the lubricating state of the seal surface and to attain enhancement in the wear-proofness.
Besides, the provision of the communicating slot 101a, not only forms the lubricating film, but also affords the function of vomiting the foreign matter existent in the lubricating oil and the wear powder ascribable to the wear, onto the unsealed fluid side A so as not to be bitten between the first seal portion 101 and the sidewall surface of the annular groove 301, and it cools the seal surface owing to the formation of the lubricating film, thereby to attain the enhancement of the wear-proofness still more.
Even with the seal ring according to the prior-art technique as explained above, however, the occurrence of the wear of the sidewall surface of the annular groove 301 is often found. As the result of a study by the Inventor, it has been revealed that the sidewall surface of the soft metal wears away because the foreign matter existent in the lubricating oil intervenes between the sliding surfaces.
Besides, in a case where the wear has proceeded due to a long-term use, the sidewall surface of the annular groove 301 wears away only at its part with which the first seal portion 101 is brought into sliding contact, as shown in FIG. 37, so that the seal ring 100 is pushed inwards with respect to the original position of the sidewall surface of the annular groove 301 in correspondence with a component having worn.
In addition, when the bottom surface of the communicating slot 101a has reached that plane of the sidewall surface of the annular groove 301 which is not worn, a path leading to the communicating slot 101a is cut off as indicated by an arrow X in FIG. 37, and the lubricating oil fails to be fed, so that the drawback of the occurrence of abnormal wear might take place.
In this regard, there has also been known a seal ring 400 whose sectional shape is trapezoidal as shown in FIGS. 38 and 39. The seal ring 400 has been constructed for the purpose that a seal portion 402 comes into linear contact in order to reduce sliding friction, and the seal portion 402 is formed at the upper end edge of the annular groove 301.
In case of the seal ring 400, leakage occurs through the gap Z between a convex part and a concave part in the special step cut, irrespective of whether or not the sidewall surface of the annular groove inclines. Another problem is that, since the quantity of leakage changes depending upon the inclination angle of the annular groove, a stable leakage characteristic is not obtained.
Besides, in a case where the soft metal is applied to the shaft in this seal ring, the quantity of wear of the side surface of the shaft groove is small, but the quantity of leakage thereat changes depending upon a gap To. The gap To=width of about 0.2-0.6 mm holds depending upon the dimensional tolerance of the outside diameter of the seal ring and that of the hole diameter of the housing, and the quantity of leakage in that case can become about 200-500 cc/min (0.2-0.5 l/min).
The quantity of leakage of the seal ring which has the separation portion of the general special step cut is at most 100 cc/min (0.1 l/min). In such a case as stated above, the quantity of leakage is excessive and is therefore difficult to be coped with by the ordinary capacity of a hydraulic pump.
Besides, even when the quantity of leakage is coped with by enlarging the hydraulic pump capacity in such a case, a loss developing in the hydraulic pump increases. That is, there occurs the problem that a fuel cost degrades.
The present invention has been made in order to solve the problems of the prior-art techniques, and has for its object to provide a seal ring of excellent quality which attains reduction in the quantity of leakage while reducing rotational sliding friction, and which maintains a stable sealing performance over a long term.